Electrode catheters have been in common use in medical practice for many years. They are used to stimulate and map electrical activity in the heart and to ablate sites of aberrant electrical activity. In use, the electrode catheter is inserted into a chamber of the heart. Once the catheter is positioned, the location of aberrant electrical activity within the heart is then located.
One location technique involves an electrophysiological mapping procedure whereby the electrical signals emanating from the conductive endocardial tissues are systematically monitored and a map is created of those signals. By analyzing that map, the physician can identify the interfering electrical pathway. A conventional method for mapping the electrical signals from conductive heart tissue is to percutaneously introduce an electrophysiology catheter (electrode catheter) having mapping electrodes mounted on its distal extremity. The catheter is maneuvered to place these electrodes in contact with or in close proximity to the endocardium. By monitoring the electrical signals at the endocardium, aberrant conductive tissue sites responsible for the arrhythmia can be pinpointed.
For mapping, it is desirable to have a relatively small mapping electrode. It has been found that smaller electrodes record more accurate and discrete electrograms. Additionally, if a bipolar mapping arrangement is used, it is desirable that the two electrodes of the mapping arrangement be in close proximity to each other and that they be similar in size to produce more accurate and useful electrograms.
Once the origination point for the arrhythmia has been located in the tissue, the physician uses an ablation procedure to destroy the tissue causing the arrhythmia in an attempt to remove the electrical signal irregularities and restore normal heart beat or at least an improved heart beat. Successful ablation of the conductive tissue at the arrhythmia initiation site usually terminates the arrhythmia or at least moderates the heart rhythm to acceptable levels.
A typical ablation procedure involves providing a reference electrode, generally taped to the skin of the patient. RF (radio frequency) current is applied to the tip electrode, and current flows through the media that surrounds it, i.e., blood and tissue, toward the reference electrode. Alternatively, the catheter may carry bipolar electrodes, in which instance, the current flows from the tip electrode, through the media and toward another electrode carried on the catheter tip. In any case, the distribution of current depends on the amount of electrode surface in contact with the tissue as compared to blood, which has a higher conductivity than the tissue. Heating of the tissue occurs due to electrical current. The tissue is heated sufficiently to cause cellular destruction in the cardiac tissue resulting in formation of a lesion within the cardiac tissue which is electrically non-conductive.
A disadvantage with current catheters is where the aberrant activity originates in a vein or other tubular structure leading away from the heart chamber. In the case of electrophysiological triggers in such locations, a common alternative to the ablation of the tissue that generates the triggers involves ablating a lesion to interrupt wavelets, for example, when ablating a line of block. For tubular regions in or around the heart, this procedure requires the line of block to be made about a circumference of the tubular region. However, it is difficult to manipulate and control the distal end of a straight catheter so that it effectively ablates about the circumference. Moreover, although most vessels have circular cross-sections, many do not and they come in different sizes. Accordingly, a need exists for an improved catheter that is particularly useful for such applications
Flower mapping catheters are known; however, conventional flower catheters carry smaller electrodes which are not well suited for ablation. Furthermore, existing flower catheters were developed for atrial diagnostics, not vein mapping or ablation which pose different challenges.
Lasso catheters are also known. However, lasso catheters have a generally circular main portion which is not always adaptable to noncircular tubular structures. Moreover, the generally circular main portion is typically positioned along a single circumference of the tubular structure for forming a line of isolation. As such, testing the line of isolation for completion requires repositioning the catheter, ire-use of a second catheter, both of which increase the duration, complexity and/or cost of the ablation procedure.
Thus, there is a desire for a catheter adapted for mapping and ablation in a tubular structure, especially a tubular structure with a noncircular cross-section. It is further desired that the catheter be adapted for testing completeness of ablation isolation lines without the need for repositioning or the use of an additional catheter.